Stored energy combustors have long been utilized for producing hot gases of combustion under pressure to operate turbines. In such stored energy combustors, a fuel is typically combusted with an oxidant to produce the hot gases of combustion, and additional fuel may typically be introduced into the hot gases of combustion to be vaporized, or partly decomposed, or both. By so doing, the volume of hot gas can be increased while bringing the temperature of combustion down to a temperature incapable of causing damage to the turbine.
Ignition is a most critical part of the combustion process and, in some instances, it is a requirement that ignition occur on the first spark. This is particularly true of emergency power applications, and it is, of course, a much more demanding requirement than typical combustors since it mandates a high degree of design excellence. To achieve reliable ignition, air inlet velocities at entry to the combustion zone must be low, e.g., below about 275 feet per second.
For ignition purposes, an igniter is typically located at the outer diameter of the combustor. It there provides a spark or series of sparks of significant energy level to provide ignition. Generally speaking, the fuel spray is directed to impact the igniter to achieve ignition.
Typically, in stored energy combustors, operational combustion chamber pressures reach as high as 300 psia or greater with flame temperatures reaching as high as 3800.degree. F. When the oxidant is oxygen, substantially higher temperatures are reached. From the foregoing, it will be appreciated that the igniter is continuously exposed to high temperature gases which are at relatively high velocities.
As a result of these operating conditions, the life of the igniter can be significantly shortened. If gas velocities are raised to achieve a more compact combustor, then igniter life is diminished even further and, at the same time, the ability to achieve extremely high ignition reliability such as "first spark" ignition is diminished. Still further, it is known to be desired to maintain hot combustor walls on the order of 1,000.degree. F. or greater.
In this connection, the hot combustor walls are required to avoid undesirable carbon buildup inside the combustor. This, however, means that the fit between the igniter and the combustor wall must be carefully designed for relative expansion and contraction between the combustor wall and the igniter during heat up and cool down in order to avoid undesirable leakage. For all of these reasons, it will be appreciated that there are numerous problems in connection with igniters in combustors.
Among prior igniter design efforts, Beyler et al. U.S. Pat. No. 4,023,351 utilizes a centrally disposed igniter. This igniter is not, however, cooled in any way which would successfully overcome the problems mentioned hereinabove. Likewise, Schirmer U.S. Pat. No. 2,918,118 utilizes a centrally disposed igniter. This igniter also is, likewise, not cooled in any way capable of overcoming the problems mentioned hereinabove. Still further, Williams U.S. Pat. No. 2,541,900 utilizes an igniter adjacent a swirl pipe atomizing jet to start a gas turbine engine following which a main fuel supply is activated.
While of interest, none of the foregoing igniter designs achieves enhanced performance while providing a longer life span. In contrast, the present invention is directed to overcoming one or more of the foregoing problems and achieving the resulting objectives.